Dendritic cell (DC)-based vaccines are commonly used for cancer immunotherapy. To prepare vaccines, DCs are pulsed or transfected with either: (a) defined peptides of tumor-associated antigens, (b) total protein isolated from the tumor cell, (c) autologous total RNA isolated from the tumor cell, (d) synthetic tumor-antigen-encoding mRNA, or (e) genes that encode for specific tumor-associated antigens. Introduction of tumor-associated antigen(s) and subsequent generation of mature DCs that can stimulate tumor-antigen-specific cytotoxic T lymphocytes comprise the critical steps of cancer vaccine preparation. Here, we described a method of: (a) preparing and delivering synthetic FOXP3 mRNA into human DCs, (b) generating mature DCs,